This invention relates generally to well drilling apparatus and, more particularly, to rotary and vibratory drilling apparatus.
Rotary well drilling apparatus wherein a percussive or vibratory action is provided are well known. For example, such apparatus are disclosed in U.S. Pat. Nos. 1,745,351; 1,748,341; 2,072,470; 2,241,712; and 2,667,144.
However, such conventional drilling apparatus are not entirely satisfactory for a variety of reasons. A major disadvantage of such conventional apparatus is their relatively low rate of penetration drilling. This problem is a result of several factors all of which combine to limit the speed at which a well can be drilled. More particularly, conventional drill heads tyically have a relatively low bearing pressure capacity so that the maximum downward force which can be exerted on the apparatus is limited. For this reason, conventional drill heads frequently break during operation, especially when relatively large depths are reached (for example in excess of 10,000 feet) or where relatively small diameter bores are being drilled. It is not uncommon for the removal of the entire drill apparatus to be required every day or two in order to effect repair of broken drill heads. Another factor which limits the speed of penetration of the drill apparatus results from the fact that it can be expected that during the drilling operation, materials of varying hardness will be encountered by the drill head. Thus, it is not uncommon for a harder material to be encountered by the drill head or portions of the drill head after the drilling operation has proceeded for a period of time. In such cases, a greater axial or downward force is required to compensate for such harder material. However, it is not always possible to provide such an increased force utilizing the same drill apparatus. A third factor contributing to the relatively slow penetration speed of conventional drill apparatus is that such conventional drill apparatus, such as those disclosed in the above-mentioned United States patents, provide only a relatively slow hammer action which, although serving to break or chip the material being drilled, does not do so in an efficient manner. Yet another factor which limits the penetration speed of conventional drill apparatus is the unavoidable drilling of the cutting blades provided on the drill head during the drilling operation. In this connection, as the drilling operation proceeds, the cutting blades tend to become progressively duller. This fact coupled with the difficulty in replacing the cutting blades in conventional equipment is a serious problem.
Conventional drill apparatus have still other drawbacks. For example, where several bores having different diameters must be drilled, it is necessary to employ different drill apparatus with appropriate dimensions. This of course seriously increases the cost of such drilling operations. The removal of mud as well as the broken material formed at the bottom of the bore also is not satisfactorily accomplished in conventional apparatus. Thus, such mud removal is usually accomplished utilizing pumps or the like located at the upper end of the well and as the depth of the well increases, the effectiveness of such pumps decreases.Further, in connection with the operation of conventional percussive drill apparatus, it is not uncommon for the drill apparatus to be overstressed during the operation due to the vibrations to which the apparatus is subjected. Still another problem exists in connection with conventional apparatus in the drill insertion or lowering and withdrawal operations. Thus, during insertion, the present of mud and silt impedes the lowering of the drill apparatus. Conversely, during withdrawal of the drill apparatus, a vacuum is created in the space below the drill head which impedes the withdrawal operation.